Systems referred to as power tongs have been widely used for some time in oil field installations for making and breaking connections between end threaded products which are to be united into a string by couplings which join the products end to end. Such products include sucker rods which extend downhole within tubing or casing and provide drive power for pumping petroleum to the surface. Other strings are also made up using power tongs, and these include tubular products in the form of tubing and casing.
As the technology has developed, the threaded connection between the elements in the string has had to become more precise and stronger because of increasing demands placed on the string. As the strings have increased in length consistent with wells drilled to greater depth, they have also encountered higher pressures, and ever higher loads and forces. More secure connections are thus needed to enable the downhole equipment to be utilized for longer periods of time, with higher reliability.
Sucker rods have pin ends which are threaded without a taper, and reliance is placed on making a shoulder connection which is properly prestressed to withstand the forces that are to be encountered in cyclic pump operation over a long duration. Tubing and casing, on the other hand, utilize tapered threads, and are subject to both internal and external forces and combinations thereof. Also, the integrity of the connection between male and female threads is a consequence not only of the degree of engagement but of the dimensional tolerances that are permissible.
An improvement in sucker rods is evidenced by U.S. Pat. No. 6,942,254 and application Ser. No. 09/960,391 of Kenneth J. Carstensen which both disclose a connection in which the end faces of the pin ends of the sucker rods engage each other either directly or via an intermediate torque disk. The connection is made up to a first operative point at which the pin ends are under initial compression and the coupling is then further tensioned to a further precise degree. This arrangement unites the component parts of the sucker rod connection in a manner such that they withstand the varying forces encountered during the action of a reciprocal or rotary pump, and resist the development of microcracks and consequent fatigue failures.
The practical economic and throughput requirements at operating wells do not justify or permit the installation of expensive and complicated systems for instrumenting the measurement of torque or displacement values. It is much preferred to utilize a torque applicator, specifically a power tong system, to apply a precise amount of torsional force so that the connection is mechanically secure and repeatable. In this regard, the sucker rod configuration of the referenced Carstensen patents places a high premium on a capability for prestressing the sucker rod connection with a high degree of precision. Also, since the same power tong must also function in the break mode (disengagement) it should perform all the needed functions as they are required.